Si 7 0 2 1 - A2 0
I
2
C H
UMIDITY A N D
T
EMPERATURE
S
ENSOR
Features
Precision Relative Humidity Sensor
± 3% RH (max), 0–80% RH
High Accuracy Temperature Sensor
±0.4 °C (max), –10 to 85 °C
0 to 100% RH operating range
Up to –40 to +125 °C operating
range
Wide operating voltage
(1.9 to 3.6 V)
Low Power Consumption
150 µA active current
60 nA standby current
Factory-calibrated
I
2
C Interface
Integrated on-chip heater
3x3 mm DFN Package
Excellent long term stability
Optional factory-installed cover
Low-profile
Protection during reflow
Excludes liquids and particulates
Ordering Information:
See page 29.
Applications
Pin Assignments
Micro-environments/data centers
Automotive climate control and
defogging
Asset and goods tracking
Mobile phones and tablets
HVAC/R
Thermostats/humidistats
Respiratory therapy
White goods
Indoor weather stations
Top View
SDA
GND
DNC
1
2
3
6
5
4
SCL
VDD
DNC
Description
The Si7021 I
2
C Humidity and Temperature Sensor is a monolithic CMOS IC
integrating humidity and temperature sensor elements, an analog-to-digital
converter, signal processing, calibration data, and an I
2
C Interface. The patented
use of industry-standard, low-K polymeric dielectrics for sensing humidity enables
the construction of low-power, monolithic CMOS Sensor ICs with low drift and
hysteresis, and excellent long term stability.
The humidity and temperature sensors are factory-calibrated and the calibration
data is stored in the on-chip non-volatile memory. This ensures that the sensors
are fully interchangeable, with no recalibration or software changes required.
The Si7021 is available in a 3x3 mm DFN package and is reflow solderable. It can
be used as a hardware- and software-compatible drop-in upgrade for existing RH/
temperature sensors in 3x3 mm DFN-6 packages, featuring precision sensing
over a wider range and lower power consumption. The optional factory-installed
cover offers a low profile, convenient means of protecting the sensor during
assembly (e.g., reflow soldering) and throughout the life of the product, excluding
liquids (hydrophobic/oleophobic) and particulates.
The Si7021 offers an accurate, low-power, factory-calibrated digital solution ideal
for measuring humidity, dew-point, and temperature, in applications ranging from
HVAC/R and asset tracking to industrial and consumer platforms.
Patent Protected. Patents pending
Rev. 1.2 8/16
Copyright © 2016 by Silicon Laboratories
Si7021-A20
Si7021-A20
Functional Block Diagram
Vdd
Si7021
Humidity
Sensor
1.25V
Ref
Calibration
Memory
Control Logic
ADC
Temp
Sensor
I
2
C Interface
SDA
SCL
GND
2
Rev. 1.2
Si7021-A20
T
ABLE O F
C
ONTENTS
Section
Page
1. Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
2. Typical Application Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3. Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4. Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.1. Relative Humidity Sensor Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2. Hysteresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.3. Prolonged Exposure to High Humidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.4. PCB Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.5. Protecting the Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.6. Bake/Hydrate Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.7. Long Term Drift/Aging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5. I2C Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.1. Issuing a Measurement Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.2. Reading and Writing User Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.3. Electronic Serial Number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
5.4. Firmware Revision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.5. Heater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6. Control Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
6.1. Register Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
7. Pin Descriptions: Si7021 (Top View) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
8. Ordering Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9. Package Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.1. Package Outline: 3x3 6-pin DFN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.2. Package Outline: 3x3 6-pin DFN with Protective Cover . . . . . . . . . . . . . . . . . . . . . . 31
10. PCB Land Pattern and Solder Mask Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
11. Top Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
11.1. Si7021 Top Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
11.2. Top Marking Explanation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
12. Additional Reference Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Document Change List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Rev. 1.2
3
Si7021-A20
1. Electrical Specifications
Unless otherwise specified, all min/max specifications apply over the recommended operating conditions.
Table 1. Recommended Operating Conditions
Parameter
Power Supply
Operating Temperature
Operating Temperature
Symbol
V
DD
T
A
T
A
I and Y grade
G grade
Test Condition
Min
1.9
–40
–40
Typ
—
—
—
Max
3.6
+125
+85
Unit
V
°C
°C
Table 2. General Specifications
1.9 < V
DD
< 3.6 V; T
A
= –40 to 85 °C (G grade) or –40 to 125 °C (I/Y grade); default conversion time unless otherwise noted.
Parameter
Input Voltage High
Input Voltage Low
Input Voltage Range
Input Leakage
Output Voltage Low
Symbol
V
IH
V
IL
V
IN
I
IL
V
OL
Test Condition
SCL, SDA pins
SCL, SDA pins
SCL, SDA pins with respect to GND
SCL, SDA pins
SDA pin; I
OL
= 2.5 mA; V
DD
= 3.3 V
SDA pin; I
OL
= 1.2 mA;
V
DD
= 1.9 V
Min
0.7xV
DD
—
0.0
—
—
—
—
—
—
—
—
—
—
Typ
—
—
—
—
—
—
150
90
0.06
0.06
3.5
3.5
3.1 to 94.2
Max
—
0.3xV
DD
V
DD
1
0.6
0.4
180
120
0.62
3.8
4.0
4.0
—
Unit
V
V
V
μA
V
V
μA
μA
μA
μA
mA
mA
mA
Current
Consumption
I
DD
RH conversion in progress
Temperature conversion in progress
Standby, –40 to +85 °C
2
Standby, –40 to +125 °C
2
Peak I
DD
during powerup
3
Peak I
DD
during I
2
C operations
4
Heater Current
5
I
HEAT
Notes:
1.
Initiating a RH measurement will also automatically initiate a temperature measurement. The total conversion time will
be t
CONV
(RH) + t
CONV
(T).
2.
No conversion or I
2
C transaction in progress. Typical values measured at 25 °C.
3.
Occurs once during powerup. Duration is <5 msec.
4.
Occurs during I
2
C commands for Reset, Read/Write User Registers, Read EID, and Read Firmware Version. Duration is
<100 µs when I
2
C clock speed is >100 kHz (>200 kHz for 2-byte commands).
5.
Additional current consumption when HTRE bit enabled. See Section “5.5. Heater” for more information.
4
Rev. 1.2
Si7021-A20
Table 2. General Specifications (Continued)
1.9 < V
DD
< 3.6 V; T
A
= –40 to 85 °C (G grade) or –40 to 125 °C (I/Y grade); default conversion time unless otherwise noted.
Parameter
Conversion Time
1
Symbol
t
CONV
Test Condition
12-bit RH
11-bit RH
10-bit RH
8-bit RH
14-bit temperature
13-bit temperature
12-bit temperature
11-bit temperature
Min
—
—
—
—
—
—
—
—
—
—
—
Typ
10
5.8
3.7
2.6
7
4
2.4
1.5
18
—
5
Max
12
7
4.5
3.1
10.8
6.2
3.8
2.4
25
80
15
Unit
ms
Powerup Time
t
PU
From V
DD
≥
1.9 V to ready for a
conversion, 25 °C
From V
DD
≥
1.9 V to ready for a
conversion, full temperature range
After issuing a software reset
command
ms
Notes:
1.
Initiating a RH measurement will also automatically initiate a temperature measurement. The total conversion time will
be t
CONV
(RH) + t
CONV
(T).
2.
No conversion or I
2
C transaction in progress. Typical values measured at 25 °C.
3.
Occurs once during powerup. Duration is <5 msec.
4.
Occurs during I
2
C commands for Reset, Read/Write User Registers, Read EID, and Read Firmware Version. Duration is
<100 µs when I
2
C clock speed is >100 kHz (>200 kHz for 2-byte commands).
5.
Additional current consumption when HTRE bit enabled. See Section “5.5. Heater” for more information.
Table 3. I
2
C Interface Specifications
1
1.9
V
DD
3.6 V; T
A
= –40 to +85 °C (G grade) or –40 to +125 °C (I/Y grade) unless otherwise noted.
Parameter
Hysteresis
SCLK Frequency
2
SCL High Time
SCL Low Time
Start Hold Time
Start Setup Time
Symbol
V
HYS
f
SCL
t
SKH
t
SKL
t
STH
t
STS
Test Condition
High-to-low versus low-to-
high transition
Min
0.05 x V
DD
—
0.6
1.3
0.6
0.6
Typ
—
—
—
—
—
—
Max
—
400
—
—
—
—
Unit
V
kHz
µs
µs
µs
µs
Notes:
1.
All values are referenced to V
IL
and/or V
IH
.
2.
Depending on the conversion command, the Si7021 may hold the master during the conversion (clock stretch). At
above 100 kHz SCL, the Si7021 may also hold the master briefly for user register and device ID transactions. At the
highest I
2
C speed of 400 kHz the stretching will be <50 µs.
3.
Pulses up to and including 50 ns will be suppressed.
Rev. 1.2
5
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